1. Field of the Invention
The present invention relates to a heat exchange system for use on an electric vehicle, provided with a hot water circuit to be used for air-conditioning heating operation for previously heating, with hot water, air to a predetermined temperature to be discharged into a passenger's compartment.
2. Description of the Related Art
In general, the electric vehicle adopts the heat pump system as a heat exchange system for air-conditioning heating operation, based on the use of a high temperature and high pressure cooling medium discharged from a compressor in a refrigerating cycle. In this system, the hot water, which serves as a heating medium, is allowed to circulate through a circulation pipe by the aid of a water pump. The hot water is heated by the high temperature and high pressure cooling medium, and it is supplied to a heater core. The air, which passes through the heater core, is heated to a predetermined temperature by means of heat exchange effected between the hot water and the air.
The electric vehicle uses a heat exchange system to be used for air-conditioning cooling operation for cooling a motor for driving the vehicle and a battery for supplying electric power to the driving motor. In the cooling heat exchange system, the cooling water is allowed to circulate through a circulation pipe which communicates with a circulation passage for cooling the driving motor and the battery disposed in a battery-accommodating box. The temperature of the cooling water is lowered by allowing the cooling water at a high temperature to pass through a heat exchanger such as a radiator so that heat exchange is performed between the cooling water and external air.
The heating heat exchange system generally comprises a reserve tank which is branched from the circulation pipe, in conformity with the requirement for water supply and increase in water pressure caused by the increase in water temperature in the circulation pipe. The heating heat exchange system is devised such that the hot water is drained and supplemented by appropriately using the circulation pipe and the reserve tank. On the other hand, the cooling heat exchange system is provided with a reserve tank which communicates with the heat exchanger, because of the same reason as described above.
However, the hot water circuit for the heating heat exchange system is provided independently from that for the cooling heat exchange system, and the respective reserve tanks are disposed individually, because of the following reason. That is, in the case of the heating heat exchange system, the water temperature setting is 60.degree. C. to 80.degree. C. in a region ranging from the circulation pipe to the inside of the reserve tank in order to perform the air-conditioning heating operation. On the other hand, in the case of the cooling heat exchange system, the water temperature setting is not more than 60.degree. C. in a region ranging from the circulation pipe to the inside of the reserve tank in order to perform the air-conditioning cooling operation.
Therefore, in the case of the electric vehicle, the water supply operation is performed for each of the reserve tanks provided individually for the heating heat exchange system and the cooling heat exchange system respectively. A problem is pointed out that the water supply operation is considerably complicated. Further, an inconvenience arises in that the production cost and the installation space are increased because the two reserve tanks are used.
The heating heat exchange system includes the reserve tank which is branched from the circulation pipe. Therefore, the reserve tank has no air-vent function, although the heat loss due to heat radiation from the reserve tank is decreased. For this reason, it is necessary to separately provide an air-vent valve at an intermediate position of the pipework. A problem is pointed out that the structure of such a heating heat exchange system is complicated.